It has been found in a moment-resisting building having a structural steel framework, that most of the energy of an earthquake, or other extreme loading condition, is absorbed and dissipated, in or near the beam-to-column joints of the building.
In the structural steel construction of moment-resisting buildings, towers, and similar structures, most commonly in the past, the flanges of beams were welded to the face of columns by full-penetration, single bevel, groove welds. Thus, the joint connection was comprised of highly-restrained welds connecting a beam between successive columns. Vertical loads, that is, the weight of the floors and loads superimposed on the floors, were and still are assumed by many to be carried by vertical shear tabs or pairs of vertical, structural angle irons arranged back-to-back, bolted or welded to the flange of the beam and bolted or welded to the face of the column.
In the prior art, the greater part of the vertical load placed upon a beam was commonly assumed to carried by a shear tab bolted or welded to the web of the beam and bolted or welded to the face of the flange of the column at each end of the beam. Through the use of face-to-face gusset plates welded to the beam and, also, welded to the column, the greater part of the vertical load is carried by the gusset plates, rather than by the shear tab.
Experience has shown that the practice of welding the beam""s flanges directly to the column is uncertain and/or unsuitable for resistance to earthquakes, explosions, tornadoes and other disastrous events. Such connection means and welding practice has resulted in sudden, fractured welds, the pulling of divots from the face of the column flange, cracks in the column flange and column web, and various other failures.
Such highly-restrained welds do not provide a reliable mechanism for dissipation of earthquake energy, or other large forces, and can lead to brittle fracture of the weld and the column, particularly the flange of the column and the web of the column in the locality of the beam-to-column joint, (known as the xe2x80x9cpanel zonexe2x80x9d).
It is desirable to achieve greater strength, ductility and joint rotational capacity in beam-to-column connections in order to make buildings less vulnerable to disastrous events.
In the case of earthquakes, greater connection strength, ductility and joint rotational capacity are particularly desirable in resisting sizeable moments in both the lateral and the vertical plane. That is, the beam-to-column moment-resisting connections in a steel frame building, in an earthquake, are subjected to large rotational demands in the vertical plane due to interstory lateral building drift.
Engineering analysis, design and full-scale specimen testing have determined that prior steel frame connection techniques can be substantially improved by strengthening the beam-to-column connection in a way which better resists and withstands the sizeable beam-to-column, joint rotations which are placed upon the beam and the column.
That is, the beam-to-column connection must be a strong and ductile, moment-resisting connection.
Reference is made hereby to my U.S. Pat. Nos. 5,660,017 and 6,138,427, and my pending patent application Ser. No. 09/280,136, all mentioned above, for further discussion of prior practice and the improvement of the structural connection between beam and column through the use of gusset plates. Such patents and patent application are included herein by reference. U.S. Pat. No. 5,660,017 teaches the use of gusset plates extending alongside the column and the beam. U.S. Pat. No. 6,138,427 teaches the use of angle irons with gusset plates, to connect to column and/or beam. My patent application Ser. No. 09/280,136 teaches the use of braces with gusset plates connecting column to beam and brace.
This invention comprises the use of two gusset plates to attach a beam to a column, to serve as a xe2x80x9cprimary supportxe2x80x9d structure of a building, tower or similarly heavy structure. That is, the column is adapted for use as a permanent, columnar, structural support for carrying a load of the magnitude of building columnar loads or similarly heavy structural loads.
The structural joint of the invention comprises a column, (which may be a wide-flange column, a box column, a tube column or other suitable column), a beam (which may be a wide-flange beam, a box beam, a tube beam or other suitable beam) and a pair of gusset plates. It is to be understood that a box column has two flanges and two webs, as does a box beam. A tube column is closely similar to a box column, but has rounded corners. Similarly, a tube beam is closely similar to a box beam, but has rounded corners.
Although there are other structural shapes, (they are referred to as xe2x80x9cSxe2x80x9d shapes, xe2x80x9cMxe2x80x9d shapes, xe2x80x9cHPxe2x80x9d shapes, xe2x80x9cnarrow-flangexe2x80x9d shapes and even others), that may be used as columns and beams, in the steel frame industry, customary design utilizes wide-flange columns and beams because of their having substantially greater strength, stiffness, compactness and/or depth range than do other available structural shapes. xe2x80x9cCompactnessxe2x80x9d is determined by the ratio of the width of a flange to its thickness.
As to the column and beam shapes, the xe2x80x9cWxe2x80x9d shape is the one commonly used and is the shape used herein. It is known as the xe2x80x9cwide-flangexe2x80x9d shape. Other shapes are available and might be found suitable in certain designs, such as the xe2x80x9cSxe2x80x9d shape, xe2x80x9cMxe2x80x9d shape, xe2x80x9cHPxe2x80x9d shapes and even others.
The gusset plates in this invention face each other and extend from the column along opposing sides of the beam. One end of each gusset plate is welded to the flange of the column. In turn, the gusset plates are fixed with respect to the beam. In a preferred embodiment, the gusset plates are welded directly to the beam or welded to cover plates which are, in turn, attached to the beam by welds or fasteners.
The welds herein between the gusset plates and other members of the structural connection may be fillet welds, full-penetration groove welds, partial-penetration groove welds, flare-bevel groove welds or any other suitable weld which may be made by shielded metal arc welding, flux cored arc welding, electroslag welding, submerged arc welding or made by any other suitable welding technique within the requirements determined by a design engineer skilled in the art.
Commonly, groove welds between two structural elements entail one of the elements being beveled along its edge to be welded. The welds and techniques mentioned above are those commonly known as suitable welds and techniques in structural steel design. However, if additional suitable welds or weld types or techniques are available or become available, it is intended to cover such weld types or techniques as alternatives to the welds shown or discussed herein.
The mention or illustration of a particular kind of weld or particular kinds of welds, in the examples shown and discussed herein, is not intended to exclude the possible use of other kinds of welds which a skilled structural engineer would find suitable.
Full-penetration groove welds extend the full thickness of the element being welded. Partial-penetration groove welds customarily extend to half the thickness of the element being welded to xc2xeths the thickness of the element being welded, although the amount of partial-penetration may be less or more than these amounts, within the requirements determined by a design engineer skilled in the art. The element being welded is usually suitably beveled so as to provide space for the weld.
This invention increases both the lateral and vertical, load-carrying stability and capability of the steel frame structure. The invention herein provides such capability, providing both a lateral and vertical load moment-resisting connection and increased vertical load-carrying capability. Further, this invention complies with the industry""s current steel moment-resisting frame guidelines contained in Federal Emergency Management Agency (FEMA) guidelines (FEMA publications 350 and 351).
Consequently, the improved design of the invention is capable of carrying greater loads and capable of withstanding greater earthquakes and other calamities which may place extreme strain on a structure.
The beam-to-column connection invention herein may be made in the shop under controlled conditions and placed in new constructions or constructed in the field for new or retrofit constructions. Shop fabrication provides for better quality construction of a beam-to-column connection by reason of better control of the welding process and easier access to and handling of all parts of the connection. The invention effectively makes use of fillet welds, as well as full-penetration, partial-penetration groove welds, flare-bevel groove welds and any other suitable welds, all of which are better made under shop conditions, although they can suitably be made in the field, at greater expense and likely with less quality. Beam splices can be used in the field for erection purposes. Such splice connections when used are commonly located at structural points of reduced flexural stress. That is, the splice connections are located at some distance from the beam-to-column connection.
In some instances, bolting and angle irons may be used to connect beams to gusset plates. The word xe2x80x9cfastenersxe2x80x9d means herein xe2x80x9cboltsxe2x80x9d or xe2x80x9crivetsxe2x80x9d. xe2x80x9cFastenedxe2x80x9d means attached by means of xe2x80x9cfastenersxe2x80x9d. xe2x80x9cAttachedxe2x80x9d means xe2x80x9cweldedxe2x80x9d, xe2x80x9cboltedxe2x80x9d or xe2x80x9crivetedxe2x80x9d.
Structural steel buildings can also be constructed using a beam length which extends from one column to the next, without having to splice beam sections together. It is common to use long column sections, requiring fewer splices in the column.
The structural elements in my invention are likely to be made from steel known as ASTM A 572, Grade 50 or ASTM A 992 structural steel specification, except for the bolts and washers. High-strength aluminum and other high-strength metals and alloys might be found suitable under some circumstances.
It is to be appreciated that more than one beam may be connected to a column. For example, one beam could be connected on one side of a column and another beam could be connected on the opposing side of the column. Also, beams may be connected on four sides of a column in a biaxial application. That is, if, for example, the column is a box column, a joint connection to a respective beam could be made to each of potentially four flanges of the box column. In such case, there would be four beams, one extending in each direction away from the column. Another example of a biaxial application is a built-up cruciform column, (a multi-flanged column having as many as four flanges), wherein a joint connection to a respective beam could be made to as many as each of the flanges of the cruciform column. One example is a corner, two-sided beam-to-column connection comprising two mutually orthogonal column flanges. Another example is a three-sided beam-to-column connection comprising three column flanges. Still another example is a four-sided beam-to-column connection comprising all four column flanges.
It is to be realized in the discussion of the drawings and in the specification and claims that elements described as xe2x80x9chorizontalxe2x80x9d and xe2x80x9cverticalxe2x80x9d are with respect to the drawings as shown and such elements may be disposed at other angles and orientations depending on the construction of the structure involved. At times, columns are disposed at other than purely vertical angles and the elements would then also be at other than purely xe2x80x9chorizontalxe2x80x9d and xe2x80x9cverticalxe2x80x9d angles.
It is, therefore, an object of this invention to provide an improved structural joint connection between a beam and a column, through the use of gusset plates.
It is another object of this invention to provide an improved structural joint connection between a beam and a column through the use of gusset plates extending from the column along the sides of the beam.
Still another object of this invention is to provide an improved structural joint connection through the use of fillet welds, full-penetration welds, partial-penetration groove welds, flare-bevel groove welds or any other suitable weld between gusset plates and column.
And another object of this invention is to provide fixed attachment between two gusset plates and a column, by welding the vertical edge of each gusset plate, (the gusset plate edge parallel to the longitudinal axis of the column), to a flange of the column.